Responding to the need for stage mobility, a cable-free platform, and the occasional large ego, church audio techs have installed wireless mics throughout their facilities; all in direct violation of Biblical edict.
However, church leaders view the drawbacks of wireless mics as negligible in light of the perceived benefits; thus, wireless mics are here to stay. Helping church audio techs improve the performance of their wireless systems is the purpose of this column. Perhaps the best way to begin is by illustrating the perils that beset the best in the business.
Bill Thrasher, audio guru extraordinaire and all-around genius, recently directed the Billy Graham Crusade in the Georgia Dome with musical guests, Take 6. As is his custom, Mr. Thrasher used only the highest quality wireless mics and tested them thoroughly before Take 6 rehearsed. The dry run was uneventful, save for the video crew’s failure to set up the Teleprompter in time for the band’s use. Being resourceful fellows, the video crew simply used video monitors fed by coax terminated in BNC connectors to allow the vocalists to see the lyrics.
After the rehearsal, once the Teleprompters were in place, the video monitors were removed. The wireless mics had worked flawlessly. Bill went to grab some food, unaware of the nightmare to come.
When the actual event began, Take 6 sang impeccably, but no one heard them. The entire audio feed consisted of hideous noise, with no detectable musical content. Now in full emergency mode, the crack audio team searched diligently, but vainly, for the cause of the interference.
Seventy thousand people sat in frustration as six of the most talented voices on earth were obviated by continuous noise. At the sermon’s conclusion, Bill and the other team members began a systematic troubleshooting of the entire system.
At 4:00AM, someone discovered the unterminated BNC coax feed had never been shut off, allowing RF to spray directly at the wireless mic transmitters! The video crew, thereafter lovingly referred to as “Vidiots,” had failed to turn off the video feed after the rehearsal. The moral of the story is this: “If Bill Thrasher and a professional audio crew have wireless woes, you will too.” An alternative moral might be, “He who wields the higher RF spectrum is not always possessed of a correspondingly higher intellect.”
Occasional wireless system failure is inevitable. Constant wireless problems are avoidable if the systems are properly matched and set up. System matching involves the relationship of the individual mic frequencies to each other and to the competing RF transmissions in the local area. A wireless mic may state its operational frequency as 182.000MHz, but it will generate additional harmonic frequencies based on the fundamental of 182.000MHz. These harmonics may interfere with the harmonics of other, seemingly compatible, units.
In addition, certain systems will exhibit a broader spread of signal onto adjacent frequencies than other, more controlled, systems. These “careless” units will cause interference where none need exist. TV stations, emergency personnel, and others also compete for space in the radio spectrum. Coexisting with all of them is a difficult, but doable task. A properly operating wireless mic that suddenly exhibits transmission/reception problems is a likely victim of outside RF invasion, assuming the usual culprits (batteries, antennas, and connectors) have been eliminated as a source of trouble. Check with local authorities to verify currently used frequencies and go to the FCC’s website (www.fcc.gov) to find the latest spectrum grab by local stations.
The usual causes of trouble are the unit’s batteries, antennas, and connectors. Referenced with the acronym BAC, it is a good idea to always “go BAC to basics” to solve wireless problems. The next issue of Wireless World will detail the solutions to these three common troublemakers. Until then, God bless.